1. Field of the Invention
This invention pertains to hydraulic drilling rigs and to power swivels of the type allowing drill pipe to be passed therethrough.
2. Description of the Prior Art
Various types of hydraulic drilling rigs have been used heretofore, U.S. Pat. Nos. 3,722,607; 3,282,357; 2,502,895 and 3,158,213 are representative of some of these rigs. Most hydraulic drilling rigs have employed more than two rams or cylinders, arranged in an array which makes removal of the drill pipe difficult. The Schaffer patent, U.S. Pat. No. 2,502,895, employs a two-cylinder rig but the rig is not suitable for handling connected, multiple lengths of pipe, such as doubles or triples.
Heretofore, tripping long lengths of pipe has been a time-consuming, costly operation requiring removal of each section of pipe from below the drill stem assembly. Another approach is shown in the Ray patent, U.S. Pat. No. 3,722,607. This patent describes a through-the-power swivel drilling rig which uses slips for gripping the pipe while rotating the pipe. This type of connection to the pipe has not been well received in the industry.